Effect Of Different Solvents And Drying Methods On Structure And Gas Properties Of Carbon Membranes

Recently, gas separation membranes have been developed fast as a kind of green separation technology. The application of polymeric membranes has been limited widely in gas separation due to being underneath the Robesen upper bound. During 60s in last century, carbon membranes are developed as a kind of novel functional membrane materials, which have broad prospects in gas separation owing to super microporous, good thermal and chemical resistance. However, they are still commercially unavailable because of some problems, i.e. high-cost, dissatisfied gas permeation and selectivities. Therefore, it is urgent to look for cheap precursors with high performance, optimize preparation process to solve the problems of carbon membranes and to speed up industrialization.In this paper, a novel cheaper poly (phthalazinone ether sulfone ketone) (PPESK), with independently intellectual property rights, has been developed to prepare carbon membranes for gas separation. PPESK derived films for gas separation were prepared with different solvents, such as NMP, CHCl3, DMAc and TCE, and different drying methods including of freeze and refrigerate drying technique. Effect of different solvents and drying methods on structure and performance of PPESK carbon membranes was investigated. At the same time, the chemical structure, microstructure and gas separation properties of these membranes were characterized by FTIR, TG, XRD, XPS, TEM, elemental analysis and gas permeation tests.The result indicated that during these four carbon membranes, one prepared with C2H2Cl4 and DMAc had poor flexibility, low selectiveities and large permeation, especially that the permeation of CO2 through DMAc membranes was rather high.However, the craft of vacuum drying had limit of industrial development; The membranes prepared with CHCl3 were flexile and had high selectivites, whose freeze drying was complex; One prepared with NMP had outstanding mechanical property and selectivity, with easy craft. Thus, NMP was the optimum solvent to prepare PPESK carbon membranes. After the carbonization of 650℃, the frozen membranes had more excellent flexibility, smaller permeation and more exceedingly good selectivity than the refrigerated ones. However, with the increase of the carbonization from 650℃to 850℃, the selectivity of refrigerated membranes was continuously rising, in the meaning time accompany with the distinct evolution that that the selectivity of the frozen membranes reduced primarily and increased after that. Summing up the above, different drying methods, the property and content of solvents resulted in the polymeric films derived from different solvents with different physical and chemical structure, which would change their variation rules during subsequent preoxidation and carbonization. As a result, the carbon membranes derived from different solvents exhibited different chemical and carbon structure, pore structure and flexibility as well as different gas permeability and selectivity.